// SPDX-License-Identifier: GPL-2.0
/*
* This file contains the base functions to manage periodic tick
* related events.
*
* Copyright(C) 2005-2006, Thomas Gleixner <[email protected]>
* Copyright(C) 2005-2007, Red Hat, Inc., Ingo Molnar
* Copyright(C) 2006-2007, Timesys Corp., Thomas Gleixner
*/
#include <linux/compiler.h>
#include <linux/cpu.h>
#include <linux/err.h>
#include <linux/hrtimer.h>
#include <linux/interrupt.h>
#include <linux/nmi.h>
#include <linux/percpu.h>
#include <linux/profile.h>
#include <linux/sched.h>
#include <linux/module.h>
#include <trace/events/power.h>
#include <asm/irq_regs.h>
#include "tick-internal.h"
/*
* Tick devices
*/
DEFINE_PER_CPU(struct tick_device, tick_cpu_device);
/*
* Tick next event: keeps track of the tick time. It's updated by the
* CPU which handles the tick and protected by jiffies_lock. There is
* no requirement to write hold the jiffies seqcount for it.
*/
ktime_t tick_next_period;
/*
* tick_do_timer_cpu is a timer core internal variable which holds the CPU NR
* which is responsible for calling do_timer(), i.e. the timekeeping stuff. This
* variable has two functions:
*
* 1) Prevent a thundering herd issue of a gazillion of CPUs trying to grab the
* timekeeping lock all at once. Only the CPU which is assigned to do the
* update is handling it.
*
* 2) Hand off the duty in the NOHZ idle case by setting the value to
* TICK_DO_TIMER_NONE, i.e. a non existing CPU. So the next cpu which looks
* at it will take over and keep the time keeping alive. The handover
* procedure also covers cpu hotplug.
*/
int tick_do_timer_cpu __read_mostly = TICK_DO_TIMER_BOOT;
#ifdef CONFIG_NO_HZ_FULL
/*
* tick_do_timer_boot_cpu indicates the boot CPU temporarily owns
* tick_do_timer_cpu and it should be taken over by an eligible secondary
* when one comes online.
*/
static int tick_do_timer_boot_cpu __read_mostly = -1;
#endif
/*
* Debugging: see timer_list.c
*/
struct tick_device *tick_get_device(int cpu)
{
return &per_cpu(tick_cpu_device, cpu);
}
/**
* tick_is_oneshot_available - check for a oneshot capable event device
*/
int tick_is_oneshot_available(void)
{
struct clock_event_device *dev = __this_cpu_read(tick_cpu_device.evtdev);
if (!dev || !(dev->features & CLOCK_EVT_FEAT_ONESHOT))
return 0;
if (!(dev->features & CLOCK_EVT_FEAT_C3STOP))
return 1;
return tick_broadcast_oneshot_available();
}
/*
* Periodic tick
*/
static void tick_periodic(int cpu)
{
if (READ_ONCE(tick_do_timer_cpu) == cpu) {
raw_spin_lock(&jiffies_lock);
write_seqcount_begin(&jiffies_seq);
/* Keep track of the next tick event */
tick_next_period = ktime_add_ns(tick_next_period, TICK_NSEC);
do_timer(1);
write_seqcount_end(&jiffies_seq);
raw_spin_unlock(&jiffies_lock);
update_wall_time();
}
update_process_times(user_mode(get_irq_regs()));
profile_tick(CPU_PROFILING);
}
/*
* Event handler for periodic ticks
*/
void tick_handle_periodic(struct clock_event_device *dev)
{
int cpu = smp_processor_id();
ktime_t next = dev->next_event;
tick_periodic(cpu);
/*
* The cpu might have transitioned to HIGHRES or NOHZ mode via
* update_process_times() -> run_local_timers() ->
* hrtimer_run_queues().
*/
if (IS_ENABLED(CONFIG_TICK_ONESHOT) && dev->event_handler != tick_handle_periodic)
return;
if (!clockevent_state_oneshot(dev))
return;
for (;;) {
/*
* Setup the next period for devices, which do not have
* periodic mode:
*/
next = ktime_add_ns(next, TICK_NSEC);
if (!clockevents_program_event(dev, next, false))
return;
/*
* Have to be careful here. If we're in oneshot mode,
* before we call tick_periodic() in a loop, we need
* to be sure we're using a real hardware clocksource.
* Otherwise we could get trapped in an infinite
* loop, as the tick_periodic() increments jiffies,
* which then will increment time, possibly causing
* the loop to trigger again and again.
*/
if (timekeeping_valid_for_hres())
tick_periodic(cpu);
}
}
/*
* Setup the device for a periodic tick
*/
void tick_setup_periodic(struct clock_event_device *dev, int broadcast)
{
tick_set_periodic_handler(dev, broadcast);
/* Broadcast setup ? */
if (!tick_device_is_functional(dev))
return;
if ((dev->features & CLOCK_EVT_FEAT_PERIODIC) &&
!tick_broadcast_oneshot_active()) {
clockevents_switch_state(dev, CLOCK_EVT_STATE_PERIODIC);
} else {
unsigned int seq;
ktime_t next;
do {
seq = read_seqcount_begin(&jiffies_seq);
next = tick_next_period;
} while (read_seqcount_retry(&jiffies_seq, seq));
clockevents_switch_state(dev, CLOCK_EVT_STATE_ONESHOT);
for (;;) {
if (!clockevents_program_event(dev, next, false))
return;
next = ktime_add_ns(next, TICK_NSEC);
}
}
}
/*
* Setup the tick device
*/
static void tick_setup_device(struct tick_device *td,
struct clock_event_device *newdev, int cpu,
const struct cpumask *cpumask)
{
void (*handler)(struct clock_event_device *) = NULL;
ktime_t next_event = 0;
/*
* First device setup ?
*/
if (!td->evtdev) {
/*
* If no cpu took the do_timer update, assign it to
* this cpu:
*/
if (READ_ONCE(tick_do_timer_cpu) == TICK_DO_TIMER_BOOT) {
WRITE_ONCE(tick_do_timer_cpu, cpu);
tick_next_period = ktime_get();
#ifdef CONFIG_NO_HZ_FULL
/*
* The boot CPU may be nohz_full, in which case the
* first housekeeping secondary will take do_timer()
* from it.
*/
if (tick_nohz_full_cpu(cpu))
tick_do_timer_boot_cpu = cpu;
} else if (tick_do_timer_boot_cpu != -1 && !tick_nohz_full_cpu(cpu)) {
tick_do_timer_boot_cpu = -1;
/*
* The boot CPU will stay in periodic (NOHZ disabled)
* mode until clocksource_done_booting() called after
* smp_init() selects a high resolution clocksource and
* timekeeping_notify() kicks the NOHZ stuff alive.
*
* So this WRITE_ONCE can only race with the READ_ONCE
* check in tick_periodic() but this race is harmless.
*/
WRITE_ONCE(tick_do_timer_cpu, cpu);
#endif
}
/*
* Startup in periodic mode first.
*/
td->mode = TICKDEV_MODE_PERIODIC;
} else {
handler = td->evtdev->event_handler;
next_event = td->evtdev->next_event;
td->evtdev->event_handler = clockevents_handle_noop;
}
td->evtdev = newdev;
/*
* When the device is not per cpu, pin the interrupt to the
* current cpu:
*/
if (!cpumask_equal(newdev->cpumask, cpumask))
irq_set_affinity(newdev->irq, cpumask);
/*
* When global broadcasting is active, check if the current
* device is registered as a placeholder for broadcast mode.
* This allows us to handle this x86 misfeature in a generic
* way. This function also returns !=0 when we keep the
* current active broadcast state for this CPU.
*/
if (tick_device_uses_broadcast(newdev, cpu))
return;
if (td->mode == TICKDEV_MODE_PERIODIC)
tick_setup_periodic(newdev, 0);
else
tick_setup_oneshot(newdev, handler, next_event);
}
void tick_install_replacement(struct clock_event_device *newdev)
{
struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
int cpu = smp_processor_id();
clockevents_exchange_device(td->evtdev, newdev);
tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
tick_oneshot_notify();
}
static bool tick_check_percpu(struct clock_event_device *curdev,
struct clock_event_device *newdev, int cpu)
{
if (!cpumask_test_cpu(cpu, newdev->cpumask))
return false;
if (cpumask_equal(newdev->cpumask, cpumask_of(cpu)))
return true;
/* Check if irq affinity can be set */
if (newdev->irq >= 0 && !irq_can_set_affinity(newdev->irq))
return false;
/* Prefer an existing cpu local device */
if (curdev && cpumask_equal(curdev->cpumask, cpumask_of(cpu)))
return false;
return true;
}
static bool tick_check_preferred(struct clock_event_device *curdev,
struct clock_event_device *newdev)
{
/* Prefer oneshot capable device */
if (!(newdev->features & CLOCK_EVT_FEAT_ONESHOT)) {
if (curdev && (curdev->features & CLOCK_EVT_FEAT_ONESHOT))
return false;
if (tick_oneshot_mode_active())
return false;
}
/*
* Use the higher rated one, but prefer a CPU local device with a lower
* rating than a non-CPU local device
*/
return !curdev ||
newdev->rating > curdev->rating ||
!cpumask_equal(curdev->cpumask, newdev->cpumask);
}
/*
* Check whether the new device is a better fit than curdev. curdev
* can be NULL !
*/
bool tick_check_replacement(struct clock_event_device *curdev,
struct clock_event_device *newdev)
{
if (!tick_check_percpu(curdev, newdev, smp_processor_id()))
return false;
return tick_check_preferred(curdev, newdev);
}
/*
* Check, if the new registered device should be used. Called with
* clockevents_lock held and interrupts disabled.
*/
void tick_check_new_device(struct clock_event_device *newdev)
{
struct clock_event_device *curdev;
struct tick_device *td;
int cpu;
cpu = smp_processor_id();
td = &per_cpu(tick_cpu_device, cpu);
curdev = td->evtdev;
if (!tick_check_replacement(curdev, newdev))
goto out_bc;
if (!try_module_get(newdev->owner))
return;
/*
* Replace the eventually existing device by the new
* device. If the current device is the broadcast device, do
* not give it back to the clockevents layer !
*/
if (tick_is_broadcast_device(curdev)) {
clockevents_shutdown(curdev);
curdev = NULL;
}
clockevents_exchange_device(curdev, newdev);
tick_setup_device(td, newdev, cpu, cpumask_of(cpu));
if (newdev->features & CLOCK_EVT_FEAT_ONESHOT)
tick_oneshot_notify();
return;
out_bc:
/*
* Can the new device be used as a broadcast device ?
*/
tick_install_broadcast_device(newdev, cpu);
}
/**
* tick_broadcast_oneshot_control - Enter/exit broadcast oneshot mode
* @state: The target state (enter/exit)
*
* The system enters/leaves a state, where affected devices might stop
* Returns 0 on success, -EBUSY if the cpu is used to broadcast wakeups.
*
* Called with interrupts disabled, so clockevents_lock is not
* required here because the local clock event device cannot go away
* under us.
*/
int tick_broadcast_oneshot_control(enum tick_broadcast_state state)
{
struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
if (!(td->evtdev->features & CLOCK_EVT_FEAT_C3STOP))
return 0;
return __tick_broadcast_oneshot_control(state);
}
EXPORT_SYMBOL_GPL(tick_broadcast_oneshot_control);
#ifdef CONFIG_HOTPLUG_CPU
void tick_assert_timekeeping_handover(void)
{
WARN_ON_ONCE(tick_do_timer_cpu == smp_processor_id());
}
/*
* Stop the tick and transfer the timekeeping job away from a dying cpu.
*/
int tick_cpu_dying(unsigned int dying_cpu)
{
/*
* If the current CPU is the timekeeper, it's the only one that can
* safely hand over its duty. Also all online CPUs are in stop
* machine, guaranteed not to be idle, therefore there is no
* concurrency and it's safe to pick any online successor.
*/
if (tick_do_timer_cpu == dying_cpu)
tick_do_timer_cpu = cpumask_first(cpu_online_mask);
/* Make sure the CPU won't try to retake the timekeeping duty */
tick_sched_timer_dying(dying_cpu);
/* Remove CPU from timer broadcasting */
tick_offline_cpu(dying_cpu);
return 0;
}
/*
* Shutdown an event device on a given cpu:
*
* This is called on a life CPU, when a CPU is dead. So we cannot
* access the hardware device itself.
* We just set the mode and remove it from the lists.
*/
void tick_shutdown(unsigned int cpu)
{
struct tick_device *td = &per_cpu(tick_cpu_device, cpu);
struct clock_event_device *dev = td->evtdev;
td->mode = TICKDEV_MODE_PERIODIC;
if (dev) {
/*
* Prevent that the clock events layer tries to call
* the set mode function!
*/
clockevent_set_state(dev, CLOCK_EVT_STATE_DETACHED);
clockevents_exchange_device(dev, NULL);
dev->event_handler = clockevents_handle_noop;
td->evtdev = NULL;
}
}
#endif
/**
* tick_suspend_local - Suspend the local tick device
*
* Called from the local cpu for freeze with interrupts disabled.
*
* No locks required. Nothing can change the per cpu device.
*/
void tick_suspend_local(void)
{
struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
clockevents_shutdown(td->evtdev);
}
/**
* tick_resume_local - Resume the local tick device
*
* Called from the local CPU for unfreeze or XEN resume magic.
*
* No locks required. Nothing can change the per cpu device.
*/
void tick_resume_local(void)
{
struct tick_device *td = this_cpu_ptr(&tick_cpu_device);
bool broadcast = tick_resume_check_broadcast();
clockevents_tick_resume(td->evtdev);
if (!broadcast) {
if (td->mode == TICKDEV_MODE_PERIODIC)
tick_setup_periodic(td->evtdev, 0);
else
tick_resume_oneshot();
}
/*
* Ensure that hrtimers are up to date and the clockevents device
* is reprogrammed correctly when high resolution timers are
* enabled.
*/
hrtimers_resume_local();
}
/**
* tick_suspend - Suspend the tick and the broadcast device
*
* Called from syscore_suspend() via timekeeping_suspend with only one
* CPU online and interrupts disabled or from tick_unfreeze() under
* tick_freeze_lock.
*
* No locks required. Nothing can change the per cpu device.
*/
void tick_suspend(void)
{
tick_suspend_local();
tick_suspend_broadcast();
}
/**
* tick_resume - Resume the tick and the broadcast device
*
* Called from syscore_resume() via timekeeping_resume with only one
* CPU online and interrupts disabled.
*
* No locks required. Nothing can change the per cpu device.
*/
void tick_resume(void)
{
tick_resume_broadcast();
tick_resume_local();
}
#ifdef CONFIG_SUSPEND
static DEFINE_RAW_SPINLOCK(tick_freeze_lock);
static unsigned int tick_freeze_depth;
/**
* tick_freeze - Suspend the local tick and (possibly) timekeeping.
*
* Check if this is the last online CPU executing the function and if so,
* suspend timekeeping. Otherwise suspend the local tick.
*
* Call with interrupts disabled. Must be balanced with %tick_unfreeze().
* Interrupts must not be enabled before the subsequent %tick_unfreeze().
*/
void tick_freeze(void)
{
raw_spin_lock(&tick_freeze_lock);
tick_freeze_depth++;
if (tick_freeze_depth == num_online_cpus()) {
trace_suspend_resume(TPS("timekeeping_freeze"),
smp_processor_id(), true);
system_state = SYSTEM_SUSPEND;
sched_clock_suspend();
timekeeping_suspend();
} else {
tick_suspend_local();
}
raw_spin_unlock(&tick_freeze_lock);
}
/**
* tick_unfreeze - Resume the local tick and (possibly) timekeeping.
*
* Check if this is the first CPU executing the function and if so, resume
* timekeeping. Otherwise resume the local tick.
*
* Call with interrupts disabled. Must be balanced with %tick_freeze().
* Interrupts must not be enabled after the preceding %tick_freeze().
*/
void tick_unfreeze(void)
{
raw_spin_lock(&tick_freeze_lock);
if (tick_freeze_depth == num_online_cpus()) {
timekeeping_resume();
sched_clock_resume();
system_state = SYSTEM_RUNNING;
trace_suspend_resume(TPS("timekeeping_freeze"),
smp_processor_id(), false);
} else {
touch_softlockup_watchdog();
tick_resume_local();
}
tick_freeze_depth--;
raw_spin_unlock(&tick_freeze_lock);
}
#endif /* CONFIG_SUSPEND */
/**
* tick_init - initialize the tick control
*/
void __init tick_init(void)
{
tick_broadcast_init();
tick_nohz_init();
}
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